A typical prior art restraining device such as that disclosed in Jikkai Sho 61-132146 comprises a fixed side, a seat secured to the fixed side, and right and left arm bars. The right and left arm bars are pivotally attached to the fixed side at points located behind the seat so that they may pivot in vertical planes about an axis extending transverse to the front-to-rear axis of the vehicle. At the free end of each of the arms a horizontal bar is provided and when the right and left arm bars are lowered the horizontal bars extend toward each other across the front of the operator. This arrangement is bulky and gives the operator a sense of confinement. Also, it requires a relatively strong lifting force and long lifting stroke.